The present invention relates in general to a power converting device and, more particularly, to a power converting device of the type which supplies power to an electric car, such as a railroad car or the like.
In prior power converting devices, there has been a problem that a higher harmonic component issued from an inverter to an induction motor of an electric car flows over the body of the electric car through a stray capacity between the armature winding of the induction motor and the motor frame to exert an adverse effect, leading to a malfunction of a signal device on the ground. In the technique, as disclosed in Japanese Patent Laid-Open No. 193001/1992, the power line of an electric motor, through which the higher harmonic current will flow, is accommodated in a conductive duct so as to prevent the higher harmonic current from flowing to the car body, whereby the magnetic flux may be eliminated by connecting the motor frame electrically with the conductive duct and by using this duct as a feedback passage for the higher harmonic current.
In the prior technique described above, however, leakage of the higher harmonic current to the car body cannot be decreased to a sufficient extent.
This is because the electric motor or a heavy component having a weight of several hundreds Kg is mounted on the truck of the electric car by means of bolts or the like so that the higher harmonic current will leak to the car body through those bolts and the truck.
Thus, the higher harmonic current flowing through the car body has caused a problem in that a signal device on the ground or on the car is adversely affected by this higher harmonic component.